Day 14 - Event-driven GPIO Driver

📅 Date

YYYY-MM-DD

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🎯 Goal

Convert GPIO driver into event-driven model with:

• IRQ + deferred work
• Event queue
• Blocking / non-blocking read
• poll support

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✅ What I Learned

1. Event-driven design

• read() returns events, not state
• behaves like stream

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2. ISR design

• ISR must be minimal
• use deferred work

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3. Debounce

• use delayed_work
• avoid false triggers

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4. Ring buffer

• FIFO queue
• avoid losing ordering

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5. Blocking read

• wait queue instead of busy loop

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6. Non-blocking behavior

• return -EAGAIN

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7. poll/select integration

• enables event-driven user-space design

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8. Driver removal

• wake up readers
• return -ENODEV

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🐞 Issues Encountered

1. llseek compile error

• no_llseek not available
• replaced with noop_llseek

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2. O_NONBLOCK logic bug

• fixed condition inversion

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3. wait_event condition

• added shutting_down

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🧠 Reflection

This driver is no longer a simple char device.

It behaves like:

• input driver
• event device
• asynchronous system component

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🚀 Next Step (Day 15)

• poll / select / epoll deep dive
• user-space event loop
• multi-device monitoring